Multi-mode waveguide system



June 17,1958 GIBSON 2,839,729

MULTI-MODE WAVEGUIDE SYSTEM Filed Feb. 15, 1954 v 2 Sheets-Sheet 1Hen/i:- mpur A IN V EN TOR. JOHN .1 6/550 MM [6M June 17, 1958 J. J.GIBSON MULTI-MODE WAVEGUIDE SYSTEM 2 Sheets-Sheet 2 Filed Feb. 15. 19547'0 i/Y/i/Y/Yfl Jaw/b 62%; Mr

INVENTOR.

2,839,729 MULTI-MODE WAVEGUIDE SYSTEM John 3'. Gibson, Princeton, N. .L,as signor to Radio Corporation of America, a corporation of DelawareApplication February 15, 1954,.Serial No.f41o,302

The terminal fifteen years ofthe term of :thepat'ent to be granted hasbeen disclaimed 11 Claims. (Cl. 333-6) This invention relates 'to amulti-mode waveguidesystern, and particularly to means providingseparate couplings for each of three decoupled signals in a singlewaveguide. A different construction for a similar purpose is shown inPatent No. 2,709,240, issued to me on May 24, 1955. r 1

While not limited thereto, this invention is particularly useful in thefield of television broadcasting where separate transmitters are used togenerate the sound-modulated and the picture-modulated radio frequencysignals, and a single antenna is employed to radiate the combined orcomposite radio frequency signal. It is important that the means forcoupling the two transmitters to the common antenna be such as toisolate the transmitters from each other, and to direct energyreflectedtrom the antenna (clue to mismatch) to a soak-up resistorrather than back to the picture transmitter.

A very effective way to feed high power ultra-high frequency signals toa radiating antenna is by'means of awaveguide. A waveguide can transmitvery high power, and at ultra-high frequencies, waveguides have moderatephysical dimensions which make'them inexpensive and practical.Ultra-high frequency antenna arrays preferably include waveguide systemshaving a' plurality of radiating slots, or dipoles or monopoles. Onesuch antenna is shown and described in the U, S. Patent No. 2,807,018issued to Oakley M. Woodward, Jr., onSeptember 17, 1957. The waveguidesystem of this invention is particularly useful in coupling twotransmitters to an an tenna array of the type including a centralwaveguide from which energy is coupled to the-radiating elements of theantenna array. 1 I

An object of the invention isto provide a diplexer for I combining twoseparate radio frequency signals in a single waveguide.

Another object of this invention is to provide an ,im-

proved. system employing separate couplings for each of three decoupledsignals in a single waveguide;

Itis another object to provide an improved single waveguide systemwithin which three decoupled signals may be propagated, and threeindividual transmission l'mes connected to the single waveguide toselectively couple thru the three signals in the single waveguide.

It is a further object to provide a waveguide system including agenerally circular waveguide whichat one end forms an integral part ofan antenna array and which at the other. end is connected to threerectangular waveguides, two of which are adapted to be connected to therespective outputs of two radio transmitters, and the third of which isadapted :to be connected to a soakup resistor which absorbs energyreflected back from the antenna. Y

It is a still further object to provide an improved wave: guide systemfor coupling the outputs of two transmitters to a singlegenerally-circular waveguide extending a considerable distance to anantenna array.

In one aspect, the invention comprises a generallvcircular waveguidecapable of propagating the TB mode a 2,839,729 Patented June 17, 19.58

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' cu1ar or polygonal cross-section. One form of generally circularwaveguide has a square cross-section. A generally circular waveguidehaving an octagonal cross-section may advantageously be employed. Theupper end of the generally circular waveguide may be connected to anantenna array. The other end of the generally circular waveguide isconnected thru a transformer ta tapered section) to a rectangularwaveguide which may, at the other end, be connected to the output of apicture signal transmitter. A magic T is arranged with .respect to thegenerally circular waveguide so that the main wave guide of the magic Tis formed around the generally circular waveguide, the E- plane armextends out at right angles with the axis of the generally circularwaveguide, and the H-plane arm of the magic .T extends downwardly inparallel spaced relation with the rectangular waveguide connected to thepicture transmitter. The H-plane wave guide is adapted to be connectedto the output of a sound signal transmitter, and the E-plane waveguideis adapted :to be connected to a soak-up resistor "for absorbingenetgy-reflecte'dtrom the antenna array. Meansare provided :for couplingenergy from the main waveguide of the magic T at points equi-distantfrom the junction to points on opposite sides in the generally circularwaveguide.

In another aspect, the waveguidesystern utilizes a generally circularwaveguide having a coaxial inner conductor so that the generallycircular waveguide is capable of propagating the TE mode and the TEM orcoaxial line mode. In both forms of the invention, the generallycircular waveguide is adapted for the propagation of two decoupledsignals in the TE modes, the two modes be ing oriented atright angleswith each other. These and other objects and aspects of the inventionwill be apparent to those skilled in the art from the following moredetailed description taken together withthe appended drawings wherein: e

Fig. l is a perspective view, partly broken away, of a waveguide systemconstructed according to the teachings of this invention and including agenerally circular wave guide which is circular or cylindrical in form;

Fig. 2 is a transverse cross-sectional view taken on the line 22 of Fig.1;

Fig. 3 is a perspective view, partly broken away, of a multi-modewaveguide system utilizing a generally circular waveguide of squarecross-section, and including .a coaxial inner conductor;

Fig. 4 is a transverse sectional view'taken on the line 4.-4 of Fig. 3;and

Fig. 5 .is a transverse sectional view taken on the line 5-5 of Fig. 3.

.array.

.A magic T includes a main rectangular waveguide 13, an E-planerectangular waveguide arm 14, and an H;- plane rectangularwaveguide-arm-IS. A known-magic 'I is shown and described starting onpage 259 of :volume 16, Microwave Mixers, of the Radiation. LaboratorySeries, 1948. The magic T has a main rectangular waveguide extending .ina straight l-ineatright an les with both the E-plane arm and the H-planearm. A-

cording to the present invention, the main waveguide 13 is formed aroundthe generally circular waveguide 10. The E-plane arm 14 is adapted forconnection to a soakup resistor, and the H-p'lane arm 15 is adapted forconnection to the output of a sound signal transmitter of a televisionstation. r 7 Energy is coupled from the main waveguide 13 to theinterior of the generally circular waveguide by means of probes 16 and17 extending thru apertures 18'and 19, respectively, into the interiorof the generally circular waveguide 10. Itwill be noted that the probes16 and 17 are equi-distant from the junction 20 of the magic T. The endsof the main waveguide 13 are short-circuited at 21 and 22 at distanceswhich are electrically in the v order of a quarter-wavelength from theprobes 16 and 17, respectively. I

In the operation of the multi-mode waveguide system shown in Figs. 1 and2, as applied to a television transmitting system, energy in the TE modefrom the picture transmitter is applied thru rectangular waveguide 12,and :thru' tapered portionll to excite the TB mode in the generallycircular waveguide 10. This energy is propagated up the generallycircular waveguide 10 to the antennaarray from which it is radiated intospace. The generally circular waveguide 10 includes fins (not shown)which translate the linearly polarized TE mode to a circularlypolarized'TE mode at the antenna. A small amountof energyis reflectedback down the generally circular waveguide 10 because, in practice, itis difiicult to match'the antenna to the circular guide over a broadfrequency band. The reflected energy is translated back to a linearlypolarized TE mode by the fins.

The incident TE mode in the generally circular waveguide 10 is sooriented that it does not couple to the probes 16 and 17. The reflectedTE mode, however, is polarizedat right angles to' the incident wave, dueto the action of the fins, so that reflected energy is coupled thru theprobes 1'6Iand 17 to the two ends of the main waveguide 13 of the magicT. At an instant of time, the reflected TE mode in the generallycircular waveguide 10 couples the positive potential to probe 16 and anegative potential to probe 17. This results in energy flowing from thetwo ends of the main waveguide 13 toward the junction from whichthe'energy is coupled to the -E-plane waveguide 14. The waveguide 14 isconnected to a soak-up resistor which absorbs the energy reflected fromthe antenna. The reflected wave in the rriain waveguide 13 is soorientedthat it cannot couple to the H-plane waveguide 15 which is connected tothe sound transmitter. Energy from the sound signal transmitter isapplied in the TE mode thru the H-plane waveguide 15 to the junctionpoint 20 of the magic T. From the junction 20, the energy divides inboth directions along the main waveguide 13 and excites the probes 16and 17. The

probes. 16 and 17, at an instant of time, are both excited positively.The energy is therefore such as to excite the TM v mode in the generallycircular waveguide 10. This energy is propagated up the generallycircular waveguide -10 to the antenna from which it is radiated intospace. The sound signal energy in the H-plane waveguide 15 is sooriented that it cannot couple to the E-plane arm 14. The sound signalenergy in the generallycircular waveguide 10 is in the TM mode and isthus decoupled from "the two TE picture signals simultaneouslypropagated in opposite directions thru the generally circular waveguide10.' Y

Figs. 3, 4 and 5 show a modified form of the invention" wherein thecorresponding parts bear the same nurnerals as that used in Figs. 1 and2 except that prime designations are added. The generally circularwaveguide 10' has a square cross-section, and the main waveguide 13' ofthe magic T is formed in an angular configuration. The form of theinvention shown in Figs. 3,-'4 and 5 also ditfers from the form alreadydescribed asound-signal to the antenna array.

in that the generally circular waveguide 10' includes an --inner coaxialconductor 25 having a tapered end 26 in the tapered portion 11'.

As shown to advantage in Fig. 4, the probes 16' and 17"connect directlyto the inner conductor 25. The two TE modes in the generally circularwaveguide 10' coupled from the picture input waveguide 12 and coupled tothe reflected signal output waveguide 14' are essentially unaflEected bythe presence of the inner conductor 25 and its tapered end 26. The soundsignal applied thru the waveguide 15' and the main waveguide 13' of themagic T to the probes 16 and 17 excites theTEM or coaxialline' mode inthe generally circular waveguide 10'. This energy is then conveyed orpropagated in the coaxial line mode to the antenna.

Figs. 3 and 5 also illustrate a construction including a baflle 28extending in a plane and connecting the tapered end 26 of the innerconductor to the opposite parallel sidewalls of the tapered portion 11'.The baffie 28 lies in the equi-potential plane for the TE modepropagated thru the tapered portion 11' from the rectangular waveguide12. The baffle 28 therefore has no effect on the propagation ofthepicture signal from the transmitter to the antenna array. The baffle 28,however, serves to produce a short circuit for the reflected TE mode andto the TM mode at a location with respect to the probes 16 and 17-favorable from a bandwidth viewpoint. Furthermore, the baffle reducesthe cross-coupling between the waveguide 12 and the waveguide 13.

It will be understood that the form of the invention shown in Figs. 1and 2 may 'be modified for the propagation thru the generally circularwaveguide 10 of a coaxial line mode byincorporating the constructionshown in Figs. 3 thru- 5 including a coaxial inner conductor 25 having atapered end 26, probes 16' and 17 connected to the inner conductor 25,and a baffle plate 28. The TEM or coaxial line mode is employed for thepropagation of -By the use of the coaxial line mode for this purpose,the waveguide system is useful over a broader range of frequencies. Thisis due to the fact that the coaxial line mode has no lower cut-offfrequency, whereas the TM mode has a fairly high lower cut-ofl?frequency. A waveguide system operative over a broad range offrequencies is of considerable commercial importance when, for example,it is desired to build a system for television broadcasting in such away that a structure of a given size may be used forany one of theconsiderable number of television channel frequencies.

a It will be understod that the invention is useful in applicationsother than television broadcasting and that it may be utilized forenergy flow in either direction be-' tween the generally circularwaveguide and each of the rectangular waveguides. What is claimed is: Y

1. Means to provide separate couplings for each of three decoupledsignals in a single waveguide, comprising, a generally circularwaveguide, a rectangular waveguide having one cross-sectional dimensionsmaller thanv the cross-sectional dimension of said generally circularwaveguide, a waveguide transition connecting one end of said generallycircular waveguide to one end of said rectangular waveguide, a magic Thaving a main wave guide, an 'E-plane arm and an H-plane arm connectedtogether ata junction, said main waveguide being formed aroundsaid'generally circular waveguide, and means coupling energy from saidvmain waveguide at points equi-distant from said junction to points onopposite sides of said generally circular waveguide.

2. The combination as defined in claim 1 wherein said H-plane arm ofsaid magic T is arranged in parallel spaced relation with saidrectangular waveguide, the plane of the larger sidewall of one beingparallel with the plane of the larger sidewall of the other.

3. The combination as defined in claim 1, and in addi- Ltion, a coaxialinner conductor extending longitudinally in said generally circularwaveguide and having a tapered end in said transformer.

4. The combination as defined in claim 1 wherein said means for couplingenergy from said main waveguide to said generally circular waveguidecomprises probes extending from said main waveguide thru apertures intosaid generally circular waveguide.

5. The combination as defined in claim 4, and in addition, a coaxialinner conductor extending longitudinally in said generally circularwaveguide and having a tapered end in said transformer, said probesextending to and making contact with said inner conductor.

6. The combination as defined in claim 5, and in addition, a bafiieplate extending in a plane in both directions from said tapered end ofthe inner conductor to opposite sidewalls of said transformer.

7. A broadband high-power waveguide system for coupling the output of atelevision picture transmitter and the output of a television soundtransmitter to a single antenna, comprising, a generally circularwaveguide adapted at one endfor coupling to a transmitting antenna, arectangular waveguide having one cross-sectional dimension smaller thanthe cross-sectional dimension of said generally circular waveguide, atapered portion connecting the other end of said generally circular waveguide to one end of said rectangular waveguide, a magic T having a mainwaveguide, an E-plane arm and an H-plane arm connected together at ajunction, said main waveguide being formed around said generallycircular waveguide, a coaxial inner conductor in said generally circularwaveguide, and means coupling energy from said main waveguide at pointsequi-distant from said junction to points symmetrically disposed in saidgenerally circular waveguide.

8. A waveguide system as defined in claim 7 wherein said coupling meanscomprise transverse conductors axially aligned with each other andextending from said inner conductor thru apertures in said generallycircular waveguide on opposite sides thereof to sidewalls of said mainwaveguide.

9. A diplexer for combining two decoupled signals in a single waveguide,comprising, a generally circular waveguide, a first rectangularwaveguide having one crosssectional dimension smaller than thecross-sectional dimension of said generally circular waveguide, awaveguide transition connecting one end of said generally circularwaveguide to one end of said first rectangular waveguide, a secondrectangular waveguide wrapped at least partially around said generallycircular waveguide with the greater cross-sectional dimension parallelwith the longitudinal axis of said generally circular waveguide,

a third rectangular waveguide connected to an intermediate junctionpoint on said second rectangular waveguide, and means coupling energyfrom said second waveguide at points equi-distant from said junctionpoint to opposite sides in said generally circular waveguide, whereby TEmodes in said first and third rectangular Waveguides excite decoupledmodes in said generally circular waveguide.

10. A diplexer for combining two decoupled signals in a singlewaveguide, comprising, a generally circular waveguide, a magic T havinga main waveguide, an E-plane arm and an H-plane arm connected togetherat a junction, said main waveguide being formed around said generallycircular waveguide, and means coupling energy from said main waveguideat points equi-distant from said junction to points on opposite sides insaid generally circular waveguide, whereby TE modes in said E-plane andH-plane arms excite decoupled modes in said generally circularwaveguide.

11. A diplexer for combining two decoupled signals in a singlewaveguide, comprising a generally circular waveguide, a firstrectangular waveguide, a waveguide transition connecting one end of saidgenerally circular waveguide to one end of said first rectangularwaveguide, a second rectangular waveguide wrapped at least partiallyaround said generally circular waveguide, means for shortcircuiting theends of said second rectangular waveguide, a third rectangular waveguideconnected to said second rectangular waveguide at a point substantiallyequidistant from said ends of said second rectangular waveguide, andmeans coupling energy from said second rectangular waveguide at pointssubstantially equidistant from said ends of said second rectangularwaveguide to opposite sides in said generally circular waveguide.

O. G. June 10. 1952. PP. 659.

